For visible, physical good deeds the reward is likewise, visible. For hidden good deeds such as in one's heart and mind H'shem's rewards are also hidden, revealed in the world to come.
pg 441
Nefesh Hachaim
"For I H'shem has not changed" refers to the fact that although H'shem fills the world in the pure and unpure places, He remains the same. Just as the soul fills the body in the clean as well as unclean places and the soul still remains pure and unblemished.
Gate Three, Chapter 4 pg 112/113